Conventionally, there is a technique for play-backing a sound data in an encoded format (hereafter referred to encoded sound data) by decoding thereof in order to play-back the sound data. Usually the encoded sound data is decoded, subjected to transformation processing such as inverse quantization, inverse discrete cosine transformation (IDCT: Inverse Discrete Cosine Transform) or inverse modified discrete cosine transformation (IMDCT: Inverse Modified Discrete Cosine Transform), and sub-band filtering, IIR (Infinite impulse response) processing etc. to generate expanded data.
As techniques for accelerating decoding processing of such encoded sound data, JP 2002-58030 (Patent Literature 1), for example, discloses a decoding apparatus for encoded sound data which calculates frequency data by decoding variable length codes from the encoded sound signal for decoding scale factors and subjecting inverse quantization and then subjecting frequency-time transformation to the derived frequency data to output digital sound signals. The disclosed decoding apparatus for encoded sound data uses an IMDCT circuit to conduct the frequency-time transformation processing which at most requires computation amounts and processing time in the decoding processing, by using an IMDCT circuit to accelerate the decode processing of the sound signal.